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  NIO
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  <time datetime="2023-05-14T03:01:41.000Z" itemprop="datePublished">2023-05-14</time>
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    <a class="article-category-link" href="/categories/javase/">javase</a> / <a class="article-category-link" href="/categories/javase/I-O/">I/O</a>
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  <h1 id="NIO"><a href="#NIO" class="headerlink" title="NIO"></a>NIO</h1><hr>
<h2 id="基本概念"><a href="#基本概念" class="headerlink" title="基本概念"></a>基本概念</h2><h3 id="IO-模型"><a href="#IO-模型" class="headerlink" title="IO 模型"></a>IO 模型</h3><ul>
<li><strong>BIO 同步阻塞</strong></li>
</ul>
<p>在服务器和客户端通信的过程中，服务器线程会一直等待请求结果返回，无法处理其他请求。</p>
<ul>
<li><strong>NIO 同步非阻塞</strong></li>
</ul>
<p>在服务器和客户端通信的过程中，服务器线程可以先处理其他请求，定时检查结果是否返回。</p>
<ul>
<li><strong>AIO 异步非阻塞</strong></li>
</ul>
<p>在服务器和客户端通信的过程中，服务器线程可以先处理其他请求，客户端会主动通知服务器返回了结果。</p>
<h3 id="NIO-模式"><a href="#NIO-模式" class="headerlink" title="NIO 模式"></a>NIO 模式</h3><p>BIO 通信通常使用线程池机制实现伪异步：每建立一个连接就创建一个线程，在执行读写操作时该线程将被阻塞，直到数据流读写完成。在高并发情况下会有大量线程被创建并阻塞、CPU 将频繁切换线程，非常消耗计算机资源。</p>
<p>因此 JDK 1.4 引入了 NIO 模型，相关类存储在 java.nio 文件夹内，使用时需要进行导入。NIO 模型中，在执行读写操作时数据会先存入缓冲区，该线程可以先处理其他连接，一定时间后再对缓冲区读取或写出。</p>
<ul>
<li><p><strong>Buffer</strong>：【缓冲区】暂存将要写入或者要读出的数据。</p>
</li>
<li><p><strong>Channel</strong>：【全双工通道】对缓冲区数据读写，在通道内部支持同时读写。</p>
</li>
<li><p><strong>Selector</strong>：【选择器】用于单线程同时管理多个通道，选择器会对多个客户进行轮询，使一个线程可以同时处理多个请求。</p>
</li>
</ul>
<p>JDK 1.7 引入了 AIO 模型，相关类存储在 java.aio 文件夹内。但在 Linux 底层 AIO 实现本质仍为轮询，所以 AIO 相比于 NIO 的性能提升非常有限。目前主流的 IO 模式仍为 NIO 。</p>
<h3 id="Netty"><a href="#Netty" class="headerlink" title="Netty"></a>Netty</h3><p>Java 提供的 NIO 编程非常复杂，开发工作量和难度巨大。且可能会产生空轮询，导致 CPU 占用率 100% 。</p>
<p>于是我们引入了 Netty 开源框架封装 NIO 通信，是目前主流的使用方式。用于开发高性能高并发的 IO 程序。</p>
<hr>
<h2 id="Netty-1"><a href="#Netty-1" class="headerlink" title="Netty"></a>Netty</h2><h3 id="Netty-框架"><a href="#Netty-框架" class="headerlink" title="Netty 框架"></a>Netty 框架</h3><p>但 NIO 编程复杂自行实现 bug 极多，目前主流的 NIO 通信使用 Netty 开源框架。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">NettyOioServer</span> &#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">server</span><span class="params">(<span class="type">int</span> port)</span> <span class="keyword">throws</span> Exception &#123;</span><br><span class="line">        <span class="keyword">final</span> <span class="type">ByteBuf</span> <span class="variable">buf</span> <span class="operator">=</span> Unpooled.unreleasableBuffer(</span><br><span class="line">                Unpooled.copiedBuffer(<span class="string">&quot;Hi!\r\n&quot;</span>, Charset.forName(<span class="string">&quot;UTF-8&quot;</span>)));</span><br><span class="line">        <span class="type">EventLoopGroup</span> <span class="variable">group</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">OioEventLoopGroup</span>();</span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">            <span class="type">ServerBootstrap</span> <span class="variable">b</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">ServerBootstrap</span>();        <span class="comment">// 负责连接的池</span></span><br><span class="line"></span><br><span class="line">            b.group(group)                                    <span class="comment">//2</span></span><br><span class="line">             .channel(OioServerSocketChannel.class)</span><br><span class="line">             .localAddress(<span class="keyword">new</span> <span class="title class_">InetSocketAddress</span>(port))</span><br><span class="line">             .childHandler(<span class="keyword">new</span> <span class="title class_">ChannelInitializer</span>&lt;SocketChannel&gt;() &#123;    <span class="comment">// 初始化</span></span><br><span class="line">                 <span class="meta">@Override</span></span><br><span class="line">                 <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">initChannel</span><span class="params">(SocketChannel ch)</span> </span><br><span class="line">                     <span class="keyword">throws</span> Exception &#123;</span><br><span class="line">                     ch.pipeline().addLast(<span class="keyword">new</span> <span class="title class_">ChannelInboundHandlerAdapter</span>() &#123;            <span class="comment">//4</span></span><br><span class="line">                         <span class="meta">@Override</span></span><br><span class="line">                         <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">channelActive</span><span class="params">(ChannelHandlerContext ctx)</span> <span class="keyword">throws</span> Exception &#123;</span><br><span class="line">                             ctx.writeAndFlush(buf.duplicate()).addListener(ChannelFutureListener.CLOSE);<span class="comment">//5</span></span><br><span class="line">                         &#125;</span><br><span class="line">                     &#125;);</span><br><span class="line">                 &#125;</span><br><span class="line">             &#125;);</span><br><span class="line">            <span class="type">ChannelFuture</span> <span class="variable">f</span> <span class="operator">=</span> b.bind().sync();  <span class="comment">//6</span></span><br><span class="line">            f.channel().closeFuture().sync();</span><br><span class="line">        &#125; <span class="keyword">finally</span> &#123;</span><br><span class="line">            group.shutdownGracefully().sync();        <span class="comment">//7</span></span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"></span><br></pre></td></tr></table></figure> 
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